Infinitely variable control switch



June 26, 1956 M. J. LEWIS E'TAL 2,752,438

INFINITELY VARIABLE CONTROL SWITCH Filed Dec 28, 1953 2 1 JNVENTORS U Xf MERLE J. LEWIS &

2 N gwg MILTON .WILLIAMS.JR. s M THEIR AT ORNEY United States PatentINFINITELY VARIABLE CONTROL SWITCH Merle J. Lewis, Clinton, Iowa, andMilton S. Williams,

Jr., Louisville, Ky., assignors to General Electric Company, acorporation of New York Application December 28, 1953, Serial No.400,541

8 Claims. (Cl. 200-31) This invention relates to electric switches andmore particularly to switches of the type adapted to control the powersupplied to an electric heating element or the like.

While not limited thereto, our improved control switch is particularlyadapted to control the surface units of an electric range so that thewattage output of these units may be varied in small increments fromzero to a predetermined maximum.

Infinitely variable heat control switches wherein the amount of currentsupplied to the heating unit is regulated by intermittently interruptingthe circuit and varying the duration or frequency of the interruptionare of course well known in the art, an important advantage of suchswitches (as compared with heat control switches of the type having alimited number of separate and distinct positions to produce separateheats) being the flexibility of control afforded thereby. As disclosedand claimed in application Serial No. 400,642, filed December 28, 1953by Merle J. Lewis and Thomas H. Lennox, and assigned to the assignee ofthe present application, even greater flexibility and more precisecontrol in the low heat range may be achieved by providing a circuitinterrupter mechanism including switching means for switching theheating element controlled thereby from a relatively low voltage in oneheat range to a relatively higher voltage in another heat range. Thepresent in vention is an improvement over the prior invention of theLewis and Lennox application, and therefore we do not claim as ourinvention anything shown or described in the aforesaid Lewis and Lennoxapplication, which is to be regarded as prior art with respect to thispresent application.

A primary object of our invention is to provide an improved switch ofthe type disclosed in the aforementioned patent application having meansfor positively preventing destructive arcing between the contacts of thevoltage changing switch means.

Another object of our invention is to provide an infinitely variablecontrol switch having switch means for changing the voltage in thecircuit controlled thereby and means for positively preventing actuationof the switch means during the intervals when current is flowing in thecircuit.

Further objects and advantages of our invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims appended to and forming a part of this specification.

Briefly stated, in one embodiment of our invention we provide a pair ofmovable cooperating contacts adapted to be connected in circuit with aheating element, a constant speed cam arranged to constantly engage anddisengage the contacts, a manually adjustable cam for independentlypositioning one of the contacts so as to selectively vary the intervalsduring which they are in engagement, and a switch device operablebetween one position in which the heating element is connected to theouter 2,752,438 Patented June 26, 1956 'ice conductors of a threeconductor power source and another position in which the heating elementis connected to an outer conductor and the neutral conductor. Themanually adjustable cam includes two portions each providing separateranges of adjustment, and an actuator for the switch device so arrangedthat the heating element is energized at a relatively high voltage inone range of adjustment and a relatively lower voltage in the otherrange of adjustment. To prevent actuation of the switch device duringthe intervals when current is flowing in the circuit controlled by themovable cooperating contacts, we provide mechanical interlock meansperiodically actuated by a member carried by the shaft supporting theconstant speed cam.

For a better understanding of our invention reference may be made to theaccompanying drawing in which:

Fig. l is a fragmentary top plan view of a control switch constructed inaccordance with our invention, the cover and control knob being removed.

Fig. 2 is a fragmentary sectional view taken along the line 2-2 of Fig.1.

Fig. 3 is a plan view of another embodiment of our invention.

Fig. 4 is a side elevation view of the switch illustrated in Fig. 3.

Control switches of the character to which this invention relates areparticularly adapted to control surface heating units of electricranges, and as each surface unit must be individually controlled aseparate circuit interrupter mechanism is required for each surfaceunit. These interrupter mechanisms may be conveniently arranged around amotor operated actuator as shown in Newell Patent 2,275,918, forexample, so that the member serves as a common actuator for all theinterrupter mechanisms. Electric ranges usually have four surface unitsand accordingly the four separate circuit interrupter mechanisms may belocated respectively in the four corners of a case or housing at thecenter of which is a motor driven common actuator by which the fourinterrupter mechanisms are operated, each interrupter mechanism, howeverbeing individually adjustable by a control knob to regulate the supplyof power to the particular surface unit which it controls.

Referring to the drawing, in which Fig. 1 shows one of the circuitinterrupter mechanisms of such a multiple unit arrangement the referencenumeral 1 designates a case or housing including a bottom wall 2 and asurrounding side wall 3 which support and enclose the various elementsof the device. The housing 1 and the cover (not shown) are preferably ofinsulating material so that the various electrical conductors andterminals attached thereto are thereby electrically insulated from oneanother.

Centrally located in housing 1 is a cam 4 secured on a shaft 5 which isoperated by a constant speed motor (not shown) at a slow constant rateof speed such as one revolution per minute. Each of the circuitinterrupter mechanisms mounted in housing 1 includes a switch arm 6supported at one end on the housing by means of a flange 7 and having atits free end a cam follower 8 in operative engagement with cam 4. Camfollower 8 is biased against earn 4 by the resilience of switch arm 6and since cam 4 includes two semicircular portions the movement of arm 6is a reciprocating movement at the rate of two cycles per revolution ofshaft 5. Mounted in spaced parallel relation with respect to switch arm6 is a cooperating switch arm 9 supported at one end on housing 1 bymeans of a flanged portion 10, its free end being biased by its ownresilience into engagement with a pin 11 secured to the end of a linkmember 12. Mounted on switch arms 6 and 9 respectively are a pair ofmovable cooperating contacts 13 and 14, contact 13 being constantlyreciprocated during rotation of cam 4 toward and away from contact 14.

Link member 12 is pivotally mounted on a shaft 15 secured to housing 1and is biased so that it tends to rotate in a clockwise direction, asviewed in Fig. l, by a biasing spring 16 coiled about shaft 15 andsupported at one end in an aperture in wall 3. Link member 12 includesan arm portion 17 terminating in an enlarged portion 18 in which anadjusting screw 19 is mounted for engagement with the flange 20 ofanother link member 21. Link member 21 carries a cam follower 22 securedthereto for engagement with a manually adjustable cam member 23. Fromthe preceding description it will be evident that cam follower 22 ismoved in an arc about shaft 15 upon rotation of carn member 23 and bymeans of a linkage mechanism comprising link members 12 and 21 functionsto position contact 14 so as to selectively vary the intervals duringwhich contacts 13 and 14 are in engagement during rotation of earn 4.Cam member 23 is supported for rotation on a shaft 24 on which is alsomounted a control knob 25. Inasmuch as cam follower 22 is biased intoengagement with cam member 23 by spring 16 acting through link members12 and 21, and switch arm 9 is biased'into engagement with pin 11 onlink 12, counterclockwise movement of dam follower 22 about pivot shaft15 as a result of rotation of cam 23 causes switch contact 14 to moveaway from switch contact 13, thus shortening the intervals during whichthese contacts are in engagement. As contact 13 reciprocates toward andaway from contact 14 switch arm 9 is free to move away from pin 11during the intervals of engagement but its initial position is alwaysdetermined by the position of link member 12.

As disclosed in the. aforementioned Lewis and Lennox application theconfiguration of cam member 23 is such that it provides two ranges ofmovement of switch arm 9 and contact 14 The. cam surface of cam 23includes one portion 26 providing a plurality of contact positionsincluding a continuously disengaged position, and another portion 27providing a plurality of positions including a continuously engagedposition. The continuously disengaged position, which of coursecorresponds to the ofF position of the mechanism, is provided by a highportion 28 on cam 23 while the continuously engaged position is providedby a low portion 29 which permits switch arm 9 to move into a positionin which contact 14 is continuously engaged with contact 13 regardlessof the re cipr'ocating movement of switch arm 6. It will be observedthat portion 26 of the cam surface becomes progressively lower from highportion 28 to the beginning of portion 27, and that likewise portion 27becomes pro gressively lower from its juncture with portion 26 to lowportion 29.

In addition to switch arm 9, a contact arm 30 which moves in a planeperpendicular to the plane of movement or switch arms 6 and 9 isoperated by rotary movement of control knob 25. Contact arm 30 is fixedat one end to a support 31 integral with side wall 3 of the housing andextends inwardly toward the central portion of the housing. The free endof arm 30 extends between a pair of spaced fixed contact members whichas shown in the drawing may be a pair of spaced ring members 32 and 33supported by a suitable insulating means (not shown). Contact arm 30 isnormally biased into engagement with fixed contact 32 but may be movedinto engagement with fixed contact 33 by means now to be described.

Formed on the top surface of cam member 23 is a switch actuator 34comprising a raised flat arcuate cam surface extending in an aresubstantially equal to the arc. encompassed by carnsurface portion 27.Cooperating with switch actuator 34 is a follower 35 secured to the midportion of arm 30. It will be noted that the two ends of actuator 34terminate in inclined portions 36 and 37 which permit follower 35 totravel from the top surface of cam 23 to the raised surface of theactuator and vice versa upon rotation of cam 23. Actuator 34 ispositioned on cam 23 so that follower 35 rides on the top surface of thecam (between the two inclined portions 36 and 37) when follower 22engages cam surface portion 26, and on actuator 34 when follower 22engages cam surface portion 27. Thus actuator 34 cooperates withfollower 35 to move contact arm 30 from a first position in engagementwith fixed contact 32 when cam follower 22 engages cam portion 26 to asecond position in engagement with fixed contact 33 when cam 23 isrotated to a position in which follower 22 engages cam portion 27. Inthe drawing the parts are shown in the position in which arm 30 is heldin engagement with fixed contact 33 and cam 23 is in the range ofmovement in which follower 22 engages cam portion 27.

Referring now to the electrical circuit arrangement shown in Fig. 1, aresistance heating element 38 is connected to the control switchmechanism described above by means of wire 39 connected to terminal 40of switch arm 6 and wire 41 connected to terminal 42 of contact arm 30.Terminal 43 of switch arm 9 is connected to one of the outer conductorsof a three conductor source of power, while terminal 44 of fixed contactring 32 and terminal 45 of fixed contact ring 33 are connected to theneutral conductor and the other outer conductor of the power sourcerespectively. Thus it will be observed that contacts 13 and 14 areconnected in series with heating element 38 and that the heating elementmay be energized at a relatively high voltage or a relatively lowvoltage de pending upon whether contact arm 30 is in engagement withfixed contact 32 or fixed contact 33. While the ar-. rangement is notshown in the drawing it will be apparent to those skilled in the artthat the constant speed motor which drives shaft 5 and thus cam 4 may beconnected in circuit with an eelctric switch operated by roation ofshaft 24. With such an arrangement the motor driven shaft 5 would bedeenergized whenever cam 23 is in the off position but automaticallyenergized upon the movement of control knob 25 to any heating position.

From the preceding description it will be evident that contact arm 30 isswitched from engagement with fixed contact 32 into engagement withcontact 33 upon movement of cam 23 so that cam follower 22 engages camsurface portion 27 rather than portion 26, and that arcing betweencontacts 32 and 33 may occur if contacts 13 and 14 are closed duringswitching movement of arm 30. Further, contacts 13 and 14 may or may notbe in engagement when arm 30 is actuated depending on the position ofcam 4 at the time.

To overcome this difliculty and positively eliminate any possibility ofdestructive arcing between contacts 32 and 33, we provide a stop memberwhich may take the form of a flexible arm 46 normally interposed betweenfixed contacts 32 and 33 so that the contact arm 30 is prevented frommoving therebetween. Flexible arm 46 is secured at one end to suitablesupporting means as-. sociated with housing 1 such as an insulating ringmember 47 supported on the housing by a plurality of column member 48.Arm 46 projects radially inwardly toward the center of housing 1 andnormally occupies a position between fixed contact ring members 32 and33 in the path of movement of the free end of contact arm 30. Arm 46 isrelatively narrow as compared with distance between ring members 32 and33 and is spaced midway between the ring members so that when arm 30 isactuated it is disengaged from one of the rings but is prevented fromengaging the other ring by arm 46.

Flexible stop member 46 is arranged for movement out of the path ofmovement of contact arm 31 during each cycle of operation of contacts 13and 14, and for this purpose a rotating member 49 is secured to shaft 5for rotation therewith into periodic engagement with arm 46. Inasmuch asthe cam 4 shown in Fig. 1 provides two cycles of operation perrevolution of shaft 5, member 49 is arranged to actuate arm 46 twiceduring each revolution, and thus includes two oppositely disposedactuating portions 50 and 51. Actuating portions 50 and 51 rotate in acircular path intersecting the free end of flexible arm 46 and thus arecarried into periodic engagment with arm 46 so as to periodically moveit out of the path of movement of contact arm 30. Member 49 is orientedon shaft 5 with respect to cam 4 so that arm 46 is moved to permitactuation of contact arm 30 during the intervals when contacts 13 and 14are disengaged.

In considering the operation of the embodiment of our inventiondescribed above it will first be assumed that cam 23 is in the offposition, i. e. that high portion 28 is in engagement with cam follower22, and that a low heat output from heating element 38 is desired. Thisis obtained by rotating control knob 25 clockwise sufficiently to causecam surface portion 26 to engage follower 22 thus permitting switch arm9 and contact 14 to move toward contact 13 sufliciently to permitperiodic engagement of the contacts as cam 4 is rotated. With cam 23 inthis position follower 35 engages the top surface of the cam between thetwo ends of actuator 34 and thus the free end of contact arm 30 is inengagement with fixed contact ring 32. With control knob 25 in thisposition heating element 38 is periodically energized at a relativelylow voltage, 118 volts for example, the duration of the intervals ofengagement being dependent on the exact position of cam 23. As knob 25is rotated clockwise the intervals of engagement of contacts 13 and 14are lengthened since contact 14 is moved progressively toward contact 13by the accompanying movement of cam 23.

If a relatively high heat output is required clockwise rotation of knob25 is continued until cam portion 27 engages cam follower 22 and contactarm 30 is actuated by actuator 34 into engagement with fixed contactring 33. With the cam 23 in this range of positions heating element 38is periodically energized at a relatively high voltage, 236 volts forexample, the duration of the intervals of engagement of contacts 13 and14 depending upon the exact position of the cam 23.

During movement of cam 23 from its high voltage range to its low voltagerange the free end of contact arm 30 is disengaged from contact 33, butprevented from moving into engagement with contact 32 by flexible stopmember 46 until the heating circuit is interrupted by disengagement ofcontacts 13 and 14. Likewise, during movement of cam 23 from the low tohigh voltage range stop member 46 performs a similar function. As cam 4rotates to the position in which these contacts are momentarilydisengaged one of the actuating portions of member 49 engages the freeend of stop member 46 and flexes it out of the path of movement ofcontact arm 30. If cam 23 had previously been rotated by the operatorfrom a position in the low heat range to a position in the high heatrange, for example, contact arm 30 would be biased upwardly byengagement of actuator 34 and follower 35 and the free end of arm 30would move upwardly into engagement with contact ring 33 as soon asflexible arm 46 was withdrawn from its path of movement.

Referring now to the embodiment of the invention shown in Figs. 3 and 4,we have shown a control switch suitable for controlling a single heatingelement but it will be evident that a plurality of switch mechanisms asdisclosed in Fig. 1 might be incorporated in a device utilizing the formof our invention now to be described. Referring to Fig. 3 the numeral 52designates a base of insulating material on which a contact armsupporting member 53 is securely mounted. At the opposite end of base 52is a cam 54 secured on a shaft 55 operated by a constant speed motor(not shown) at a slow constant rate of speed such as one revolution perminute. Cam 54 co operates with a switch arm 56 supported at one end onmember 53 and having at its free end a cam follower 57 in operativeengagement with the cam surface of cam 54. Cam follower 57 is biased-against the cam by the resilience of arm 56, and since cam 54 includestwo semicircular portions the movement of arm 56 is a reciprocatingmovement at the rate of two cycles per revolution of shaft 55. Mountedin spaced parallel relation with respect to switch arm 56 is acooperating switch arm 58 supported at one end on member 53, its freeend being biased by its own resilience into engagement with a projection59 secured to the end of a link member 50. Mounted on switch arms 56 and58 respectively are a pair of movable cooperating contacts 61 and 62,contact 61 being constantly reciprocated during rotation of cam 54toward and away from contact 62.

Link member 60 is pivotally mounted on a shaft 63 secured base 52 and isbiased so that it tends to rotate in a clockwise direction, as viewed inFig. 3, by a biasing spring 64 coiled about shaft 63 and supported atone end on member 53. Link member 60 carries a cam follower 65 securedthereto for engagement with a manually ad-- justable cam member 66. Fromthe preceding description it will be evident that cam follower 65 ismoved in an are about shaft 63 upon rotation of cam member 66, and bymeans of link member 60 functions to position contact 62 so as toselectively vary the intervals during which contacts 61 and 62 are inengagement during rotation of cam 54. Cam member 66 is supported forrotation on a shaft 67 on which is also mounted a control knob 68.Inasmuch as cam follower 65 is biased into engagement with cam member 66by spring 64 acting through link member 60, and switch arm 58 is biasedinto engagement with projection 59 on link 60, counterclockwise movementof cam follower 65 about pivot shaft 63 as a result of IO tation of cam66 causes switch contact 62 to move away from switch contact 61, thusshortening the intervals during which these contacts are in engagement.As contact 61 reciprocates toward and away from contact 62 switch arm 58is free to move away from projection 59 during the intervals ofengagement but its initial position is always determined by the positionof link member 60.

Cam member 66 is similar in all respects to cam member 23 of theembodiment illustrated in Fig. l and described above. Thus the camsurface of cam 66 includes one portion 69 providing a plurality ofcontact positions including a continuously disengaged position andanother portion 70 providing a plurality of positions including acontinuously engaged position. The continuously disengaged position,which of course corresponds to the off position of the mechanism, isprovided by a high portion 71 while the continuously engaged positionisprovided by a low portion 72 which permits switch arm 58 to move intoa position in which contact 62 is continuously engaged with contac 61regardless of the reciprocating movement of switch arm 56.

In addition to switch arm 58, a contact arm 73 which moves in a planeperpendicular to the plane of movement of switch arms 56 and 58 isoperated by rotary Formed on the top surface of cam member 66 is aswitch actuator 76 comprising a raised fiat arcuate cam surfaceextending in an are substantially equal to the arc encompassed by camsurface portion 70. Cooperating with switch actuator 76 is a follower 77secured to the mid portion of arm 73. Actuator 76 is positioned on cam66 so that follower 77 rides on the top surface of the latter, betweenthe two ends of the actuator, when follower 65 engages cam surfaceportion 70 and on actuator 76 when follower 65 engages cam surfaceportion 69. Thus actuator 76 cooperates with follower 77 c arm 73 from afirst position in engage- "contact- 74' when ca'm follower ss'gen ion71516 a second position in engagement 'fcdnta'ct 75"when 'cam '66'isrotat'ed to 5150-:

to move contact men "with with sitio n fir which answer '65" engages camportion '69.

Referring now'to'the electrical circuit arrangement shod 1'1" ih' FigI'3, a' resistance heating elementi7g is connected to the control switchmechanism described asave by means'of wire '79 connected to terminal 81)of 10 and l, 62 fare iconnectedinf series with heating element 78 andthat the heating element maybe energized at a relatively high voltage ora relatively low voltage depend fixed contact fitter fixed contact 75.

From the-preceding description it will be evident that ing upon whethencontact arm 73 is in engagement with contact arm 73 is switched fromengagement with fixed' contact7d into engagement with contact 75 uponmovement"of cam"66 so that cam follower 65 engages cam surface portion70 rather than portion 69, and that arcing between contacts 74 and 75might occur of contacts 61 and 62 are closed during switching movementof arm 73 Further, contacts 61 and 62'may or may not be in engagementwhen arm 73 is actuated depending on the position of cam 54 at the time.In the present embodiment of our invention we overcome this dilficultyand positively eliminate any possibility of destructive arcing betweencontacts 74 and 75 by providing a stop member 86 carried by shaft 55 androtated into the path of a movement of the free end of contact arm 73during each interval when movable contacts 61 and 62 are in engag'ement,thus restraining arm 73 from moving'between fixed contacts 74 and 75when current is flowing in arm 73.;f As shown in Fig. 3 stop member 86may be generally oval-in form with oppositely disposed flattenedsides'87 and 88, the lon'g dimension of themember being great'enough sothat its curved periphery overlies the path o'fmovement of arm 73However when'either of flattened portions 87 or 88 are perpendicular toarm 73 thearm is free to'move between fixed contacts 74 and 75 Stopmember 86 is oriented on shaft 55 with respect to-cam 54 so thatactuation of contact arm 73 is permitted-during the intervals whencontacts 61 and 62 are disengaged.

While we have shown and described two specific embodiments ofourinvention, we do not desire our inven tion to be limited to theparticular constructions shown and described and we intendby theappended claims to cover all modifications within the true spirit andscope of'ourinvention.

What we claim as new and desire Patent-of the United States is:

1.; In a device for periodically supplying current to a heating elementor the like for selectively variable intervals of time,-the combinationof first and second movabl e cooperating contacts adapted to beconnected in circuit with said heating elementjcontinuously operablemeans for periodically moving said first contact toward and away fromsaid second contact, manually adjustable means for positioning saidsecond contact so as to selec tively vary the intervals during whichsaid contacts are in'engagementfsaid adjustable means including meansproviding first and second-ranges of movement in each of which saidsecond contact is movable to a plurality of pos itionsfswitch meansoperable bysaid adjustable to secure by Letters means as; connectingsaid heating element to a 'rela tivelylow voltage source of energy whensaid adjustable means isin said first range of movement and to arespectively. Thus it will be observed that contact (Sijustable means isin secondlrange ot m c vemer tt, amt meanso'pei'ated by 'saidcontinuously operable means rend ringsaidgswitc'h means inoperableduring the in-- tefv'alswhen'said contacts are mana emen 21" Ina'd'e'vice' for periodically supplying current to a heating element 'orthe 'like'for selectively variable intervals of time, the combination offirst and second movablefcooperating contacts adapted to be connected incircuit 'withYsaid heating element, continuously operable means forperiodically moving said first contact toward I and away from saidsecond contact, manually adjustable means for positioning said secondcontact so as to selectively vary' the intervals during which saidcontacts are in engagemenh said adjustable means including meansprovi'dinghfi r st and second ranges of movement in each of whichsaidsecond contact is movable to'a plurality of 7 positions, switch meansoperable by said adjustablemeans for connecting said heating element-toa relatively lo w-' voltage source of energy when said adjustable meansis in said first range of movement and to a relatively high voltagesource of energy when said adjustable means is;

in said second range offmovement, and means including a member carriedby said continuously operable meansfor rendering said switch meansinoperable except when said contacts are disengaged. 1

3. In a device for periodically supplying current to a heating elementor the like for selectively variable intervals of time, the combinationof first and second movable cooperating contacts adapted to be connectedin circuit with said heating element, continuously operable means forperiodically moving said first contact toward and away from said secondcontact, manually adjustable means for positioning said second contactso as to'selectively vary the intervals during which said contacts arein engagement, said adjustable means including means providing first andsecond ranges of movement in eachof which said second contact is movableto a plurality of po'- sitions, a switch actuator'movable with saidadjustable means, first andsecond fixed contacts adapted to be con-'nected to a relatively low and a relatively high voltage sourcerespectively, a movable contact arm operable by said actuator between afirst position in engagement with said first fixed contact and a secondposition in engagement with said second fixed contact, said contact armbeing adapted to be connected in circuit with said -heat-' ing element,said actuator being constructed and arranged so that said contact arm isinsaid first position when said adjustable means is in said first rangeof'movement and in said second position when said adjustable means is insaid second range of movement, a stop member normally mterposed mthe-path of movement of said contact armso as to prevent movementthereof between said first and second positions, and means forwithdrawing said stop member from said path-of movement each 'time saidfirst contact 1s m'oved'away from said second contact.

4. In'a device for periodically supplying current toa heating elementorthe like for selectively variable 'intervals oftimejthe combination offirst and second movable cooperating contacts adapted to be connected'incircuit with said heating element, continuously operable means forperiodically moving said first contact toward and away first'and secondfixed contacts adapted to be connected to 'a'relatively low and arelatively high voltage source respectively, a movable contact armoperable by said actuator between a fi'rst position in engagement withsaid first fixed contactand'a second position in engagement with said'second fixed-contact, said contact arm being adapted to be connected incircuit witl r said heat-ing ele ment, and said actuator beingconstructed and arranged so that said contact arm is in said firstposition when said adjust-able means is in said first range of movementand in said second position when said adjustable means is in said secondrange of movement, a stop member normally interposed in the path ofmovement of said contact arm so as to prevent movement thereof betweensaid first and second positions, and a continuously operable memberarranged to engage and move said stop member from said path of movementduring the intervals when said first and second contacts are disengaged.

5. In a device for periodically supplying current to a heating elementor the like for selectively variable intervals of time, the combinationof first and second movable cooperating contacts adapted to be connectedin circuit with said heating element, continuously operable means forperiodically moving said first contact toward and away from said secondcontact, linkage means including a cam follower for positioning saidsecond contact so as to selectively vary the intervals during which saidcontacts are in engagement, a manually adjustable cam member including acam surface in operative engagement with said cam follower, said camsurface including a first portion providing a plurality of positions ofsaid second contact and a second portion also providing a plurality ofsaid positions, first and second fixed contacts adapted to be connectedto a relatively low and a relatively high voltage source respectively, amovable contact arm operable between a first position in engagement withsaid first fixed contact and a second position in engagement with saidsecond fixed contact, said contact arm being adapted to be connected incircuit with said heating element, and an actuator for said contact armcarried by said cam member and arranged so that said contact arm ismoved into said first position when said first portion of said camsurface is in engagement with said cam follower and into said secondposition when second portion of said cam surface is in engagementtherewith, a flexible arm normally positioned between said fixedcontacts and in the path of movement of said contact arm so as toprevent movement thereof between said first and second positions, and amember carried by said continuously operable means into periodicengagement with said flexible arm so as to move it out of said path ofmovement during the intervals when said first and second contacts aredisengaged.

6. In a device for periodically supplying current to a heating elementor the like for selectively variable intervals of time, the combinationof first and second movable cooperating contacts adapted to be connectedin circuit with said heating element, continuously operable means forperiodically moving said first contact toward and away from said secondcontact, manually adjustable means for positioning said second contactso as to selectively vary the intervals during which said contacts arein engagement, said adjustable means including means providing first andsecond ranges of movement in each of which said second contact ismovable to a plurality of positions, and switch means operable by saidadjustable means for connecting said heating element to a relatively lowvoltage source of energy when said adjustable means is in said firstrange of movement and to a relatively high voltage source of energy whensaid adjustable means is in said second range of movement, and stopmeans carried by said continuously operable means and engageable withsaid switch means to render the switch means inoperable during theintervals when said contacts are in engagement.

7. In a device for periodically supplying current to a heating elementor the like for selectively variable intervals of time, the combinationof first and second movable cooperating contacts adapted to be connectedin circuit with said heating element, continuously operable means forperiodically moving said first contact toward and away from said secondcontact, manually adjustable means for positioning said second contact,manually adjustable means for positioning said second contact so as toselectively vary the intervals during which said contacts are inengagement, said adjustable means including means providing first andsecond ranges of movement in each of which said second contact ismovable to a plurality of positions, a switch actuator movable with saidadjustable means, first and second fixed contacts adapted to beconnected to a relatively low and a relatively high voltage sourcerespectively, a movable contact arm operable by said actuator between afirst position in engagement with said first fixed contact and a secondposition in engagement with said second fixed contact, said contact armbeing adapted to be connected in circuit with said heating element, andsaid actuator being constructed and arranged so that said contact arm isin said first position when said adjustable means is in said first rangeof movement and in said second position when said adjustable means is insaid second range of movement, and a stop member carried by saidcontinuously operable means into the path of movement of said contactarm during each interval when said movable contacts are in engagement,whereby said contact arm is restrained from moving between said fixedcontacts when current is flowing therethrough.

8. In a device for independently controlling the supply of current to aplurality of heating elements or the like, the combination of acontinuously operable cam, a separate pair of movable contacts for eachheating element, each pair of contacts having a member operable by thecam to cause intermittent engagement and disengagement of the respectivepairs of contacts, said members being uniformly spaced about the cam,separate linkage means each including a cam follower for positioning oneof each of the pairs of contacts so as to selectively vary the intervalsduring which they are in engagement, a manually adjustable cam for eachof the linkage means including a cam surface in operative engagementwith its cam follower, said cam surface including a first portionproviding a plurality of positions of the contact positioned by said camfollower including a continuously disengaged position and a secondportion providing a plurality of said positions including a continuouslyengaged position, first and second fixed contact members adapted to beconnected to a relatively low and a relatively high voltage sourcerespectively, separate movable contact arms each adapted to be connectedin circuit with one of said plurality of heating elements, said contactarms being separately operable between a first position in engagementwith said first fixed contact member and a second position in engagementwith said second fixed contact member, separate actuators for saidcontact arms carried by said manually adjustable cams and arranged sothat each contact arm is moved into said first position when the first.cam surface portion of the cam on which its actuator is carried is inengagement with its cam follower and into said second position when thesecond cam surface portion thereof is in engagement with said camfollower, and separate flexible arms each normally positioned betweensaid fixed contact members and in the path of movement of one of saidcontact arms so as to prevent movement thereof between said first andsecond positions, and a member carried by said continuously operable caminto periodic engagement with said flexible arms so as to move them outof said paths of movement during the intervals when the pairs ofcontacts respectively associated therewith are disengaged.

References Cited in the file of this patent UNITED STATES PATENTS2,194,587 Brown et al. Mar. 26, 1940 2,215,404 Myers Sept. 17,19402,294,573 Potter Sept. 1,1942 2,503,082 Tuttle Apr. 4,1950 2,572,553Wojcik Oct. 23,1951

